1. Field of the Invention
The instant invention relates to compositions comprising a water-soluble plant nutrient in a form suitable for slow, continuous release of such nutrient to the soil by the natural influence of the environment, viz rain, air, and bacteria.
2. Description of the Art
Due to the increasing demands on the agricultural industry, there is a need for supplementing plant nutrients, either by soil or foliar application. These nutrients include a variety of micronutrients, such as zinc, iron, copper, magnesium, manganese, molybdenum and boron as well as the micronutrient or fertilizers, i.e., nitrogen, phosphorus and potassium. Elemental sulfur may be utilized to supply water-soluble sulfate, an additional nutrient, and has the further advantage of reducing soil alkalinity.
It is often desirable to supplement soil concentrations of more than one of these nutrients in a single application. Thus it would be beneficial to have a single nutrient combination in an easily handleable form that would not segregate during transport or application.
Obviously, all of the nutrients could be supplied individually, and that procedure has the equally obvious advantage of allowing immediate on-site variation of nutrient concentration. However, it has the disadvantage that all nutrients are not maintained in immediate proximity to each other. In some cases this factor is not particularly significant. However, it is found that bacterial sulfur oxidation creates an acidic environment in the vicinity of the sulfur particles and that this environment can convert the insoluble oxides, carbonates and sulfides of the above micronutrients to soluble sulfates. This acidification even improves the mobility of all nutrients applied as water-soluble compounds in calcareous soils by reducing the tendency of otherwise mobile compounds to convert to immobile hydroxides, oxides, and the like. Nutrients, both micronutrients and the above macro nutrients, must be made available to the plant roots in a soluble, mobile form to allow their assimulation by the crop.
The acidizing effect of elemental sulfur applied in any reasonable dosages, e.g., 20 to 800 pounds per acre, exists only, or at least to a large extent, in the area adjacent the sulfur particle. Thus, at least in calcareous soils, soil pH will increase with distance from the particle surface. Due to this effect and the beneficial influence of sulfur acidification on nutrient mobility, particularly on the conversion of insoluble, immobile compounds to mobile forms, it would be desirable to assure that all of the applied nutrient is fixed in the immediate vicinity of, and preferably within, the sulfur particle. It is even more desirable that the nutrient compound be evenly distributed throughout the matrix of the sulfur particle to assure gradual nutrient release rather than a slugging effect that would result from alternative procedures such as surface coating a fertilizer or nutrient particle with a continuous sulfur envelope (For an example of surface coating a fertilizer particle, e.g. an oil-coated, ammonium, phosphate-nitrate with a dispersion comprising micronutrients in sulfur, see U.S. Pat. Nos. 3,295,950 and 3,342,577. Despite the fact that the sulfur-coated fertilizer particles, of these references, are disclosed as having a controlled dissolution rate, it is clear that the relatively large particle size of the water-soluble ammonium phosphate-nitrate will result in immediate release of nitrogen to the soil rather than continuous, slow release when the ammonium phosphate-nitrate is exposed, by dissolution of the sulfur envelope.)
There are a number of micronutrients sources. Some are soluble such as the sulfates, nitrates and complexes with chelating agents, all of which are known in the agricultural industry. Less expensive micro nutrients, however, can be obtained as the oxides, sulfides and carbonates, the oxides being particularly preferred due to availability and lowest cost. In U.S. Pat. Nos. 4,133,668, 4,302,237, and 4,326,875, there is disclosed a method for preparing fusions of water-insoluble micronutrients such as the above oxides, sulfides, and carbonates, in a sulfur matrix by quenching a molten mixture of sulfur and a water-insoluble micronutrients (said micro nutrient being incorporated in said sulfur as a hydrocarbon dispersion) with water. The concern with loss of water-soluble nutrients by dissolution in the water quench, utilized to comminute and solidify the molten mixture into particles, results in the absence of water-soluble nutrients combined in said fusion. Moreover, since the water quench does not substantially "wet" the molten sulfur, the surface area of the particulate sulfur fusion is not as low as desired for rapid degradation when applied to the soil as a source of nutrients.
Slurries of sulfur in oil are prepared by quenching molten sulfur in an oil bath. (See, for example, U.S. Pat. No. 3,663,478.) The patentees are concerned with pipeline transportation of sulfur and oil; therefore, there is no suggestion that water-soluble or water insoluble nutrients might be combined with the disclosed sulfur-oil slurry.
Therefore, it is one object of this invention to provide a method for producing homogeneous, solid fusions of fertilizers and in a continuous sulfur matrix.
Another object is the provision of improved, homogeneous solid fusions of fertilizers and micronutrients dispersed through a continuous sulfur matrix which assure an even, gradual nutrient release from the sulfur particles as a result of gradual bacterial oxidation.
Another object is the provision of methods for producing such solid fusions of sulfur, fertilized and, micronutrients.
Still another object is to provide high surface area particulate sulfur fusions which are more rapidly available as a source of nutrients when applied to the soil.
Other objects and advantages of the instant invention will be apparent from a careful reading of the specification below.